Conventionally used for connection between various electronic members, and particularly a connection between a liquid crystal display panel and its driving circuit is a flexible wire board having an arrangement in which a wire pattern is formed on a flexible insulating base material which is made of polymer, such as polyimide or the like.
On the flexible wire board is mounted a semiconductor device, thereby making up a semiconductor apparatus. The semiconductor device thus mounted becomes a driving circuit of a liquid crystal display panel. An example of a conventional semiconductor device connecting method is TCP (Tape Carrier Package) mounting. A flexible wire board on which a semiconductor device is mounted by the TCP mounting is, as shown in FIG. 10, arranged such that a Cu (copper) foil pattern 102 is bonded to a base polymer film 101 by a copper film adhesive layer 105. The base polymer film 101 is a flexible insulating base material made of polymer.
Further, the Cu foil pattern 102 is covered with a polymer insulating protective film 104. The insulating protective film 104 is bonded to the Cu foil pattern 102 by an insulating protective film adhesive layer 106, provided that one end of the Cu foil pattern 102 is left uncovered, i.e., not covered with the insulating protective film 104. The uncovered portion of the Cu foil pattern 102 functions as a terminal portion to connect to an external electronic member.
Here, the insulating protective film 104 insulates the Cu foil pattern 102 from the outside, protects the Cu foil pattern 102 from corrosion such as the formation of rust, and enhances resistance to bending.
On a surface of the uncovered portion of the Cu foil pattern 102 is formed a plating layer 103 which is given such plating as Au/Ni plating (i.e., an Ni layer is first formed as a base coat which is then plated with Au), Sn plating or the like. The plating layer 103 has a function to stabilize connection to an external electronic component by keeping the Cu foil pattern 102 rust free. Accordingly, the uncovered portion of the Cu foil pattern 102 becomes a terminal portion having superior conductivity.
Note that, though FIG. 10 shows an arrangement in which the base polymer film 101 and the Cu foil pattern 102 are bonded with an adhesive (copper film use adhesive layer 105), further available is an “adhesive-free” flexible wire board having an arrangement in which the base polymer film 101 and the copper foil pattern 102 are directly bonded.
Meanwhile, in accordance with a tendency in recent years to downsize outside dimensions of electronic devices of various kinds, such as a liquid crystal display device and the like, a form of mounting components which saves as larger space as possible is greatly demanded. In fulfillment of such demand, a flexible wire board as below is used in a bent state. The flexible wire board is connected to connection terminals of an electronic component, such as a liquid crystal display panel, etc., so as to supply the connection terminals with various signals including input signals from other electronic components such as a driving circuit and the like which are provided individually (i.e. so that they are segregated) from the electronic component having the connection terminals to which the flexible wire board is connected. By bending the flexible wire board, the flexible wire board can be placed in a position that does not obstruct the mounting of other electronic components. Moreover, thus bending the flexible wire board can downsize the whole device that includes a plurality of electronic components and the flexible wire board that connects them. Further, in accordance with a tendency in recent years to further downsize electronic devices of various kinds, such a flexible wire board that has as smaller radius of curvature as possible while maintaining high reliability is demanded.
In order to fulfil this demand, recently adopted as a connection method capable of mounting a semiconductor device onto the flexible wire board is COF (Chip On Film) mounting. The reason is that the COF (Chip On Film) mounting reduces a thickness of a base material of the flexible wire board more than TCP mounting does.
In the case of the TCP mounting, on one hand, a base material thickness of the base polymer film 101 which is a base material is 75 μm. On the other hand, in the case of the COF mounting, a base material thickness of the flexible wire board is as thin as 40 μm. The flexible wire board subject to the COF mounting has higher flexibility than that of the flexible wire board subject to the TCP mounting because of its thin base material, thereby being easily bent.
The flexible wire board subject to the COF mounting, however, has a problem such that a Cu foil pattern is likely to break when the flexible wire board is bent to be mounted onto a liquid crystal display panel.
More specifically, as shown in FIG. 11, in the case where a terminal portion (an uncovered portion of a Cu foil pattern 204) of a flexible wire board 203 subject to COF mounting is bent for connection to not-shown external connection terminals of a liquid crystal display panel 201, the absence of a solder resist 205 which is a protective layer in an end portion of the flexible wire board 203 allows a terminal corner 201a of the liquid crystal display panel 201 to contact terminals or a portion in the vicinity of the terminals where the Cu foil pattern 204 is exposed, thereby easily breaking wire in a portion where the contact is made.
In order to solve this problem, the uncovered portion of the Cu foil pattern 204 is conventionally fortified with resin coating or the like. However, the fortification like this inevitably increases manufacturing steps in the manufacture of the flexible wire board, thereby reducing manufacture efficiency and increasing manufacturing costs.
Further, Japanese Unexamined Patent Publication No. 138387/1997 (Tokukaihei 9-138387 published on May 27, 1997), for example, proposes a solution to the problem. Namely, an end portion of an insulating protective film to be a base material of a flexible wire board is caused to become wavy, then a bending portion of the flexible wire board is given a desirable R while maintaining a bent state, thereby dispersing stress which is added to the insulating protective film in the bending portion and suppressing emergence of a break in the wire pattern.
This arrangement, however, raises other problems. Namely, the formation of a wavy insulating protective film complicates the manufacture of the flexible wire board, which reduces manufacture efficiency and increases manufacturing costs, and also upsizes the flexible wire board by height of a wave of the wavy insulating protective film.